Adequate sexual function is a complex interaction of hormonal events and psychosocial relationships. There are four stages to sexual response as described in the International Journal of Gynecology & Obstetrics, 51(3):265–277 (1995). The first stage of sexual response is desire. The second stage of sexual response is arousal. Both physical and emotional stimulation may lead to breast and genital vasodilation and clitoral engorgement (vasocongestion). In the female, dilation and engorgement of the blood vessels in the labia and tissue surrounding the vagina produce the “orgasmic platform,” an area at the distal third of the vagina where blood becomes sequestered. Localized perivaginal swelling and vaginal lubrication make up the changes in this stage of sexual response. Subsequently, ballooning of the proximal portion of the vagina and elevation of the uterus occurs. In the male, vasodilation of the cavernosal arteries and closure of the venous channels that drain the penis produce an erection. The third stage of sexual response is orgasm, while the fourth stage is resolution. Interruption or absence of any of the stages of the sexual response cycle can result in sexual dysfunction. One study found that 35% of males and 42% of females reported some form of sexual dysfunction. Read et al, J. Public Health Med., 19(4):387–391 (1997).
While there are obvious differences in the sexual response between males and females, one common aspect of the sexual response is the erectile response. The erectile response in both males and females is the result of engorgement of the erectile tissues of the genitalia with blood which is caused by the relaxation of smooth muscles in the arteries serving the genitalia. This increase in blood flow results in vasodilation and an increase in the temperature of the genitalia tissue.
Methods for evaluating and measuring physiological changes to determine sexual arousal have been previously described. For example, U.S. Pat. Nos. 5,565,466 and 5,731,339 describe the use of Doppler ultrasound velocimetry for measuring vaginal and penile blood flow; Intl. J. Impotence Res., 9:27–37 (1997) discloses the use of photoplethysmorgraphy for monitoring vaginal blood flow; and WO 99/35968 describes devices and methods for monitoring female arousal. These prior art methods are invasive and have major limitations that can effect the accuracy of the measurements.
There is a need in the art for new and improved noninvasive methods for measuring vasodilation and changes in blood flow, and for diagnosing and monitoring diseases related to vasodilation, such as, sexual dysfunctions. The present invention is directed to these, as well as other, important ends.